In related arts, the transmission rate of a system can increase linearly with the number of antennas by a multiple-antenna spatial multiplexing technology. Although the increase in the number of antennas can improve the rate of the system significantly, it increases greatly the complexity of algorithm of a receiver. For example, the complexity of a max likelihood (referred to as “ML”) detection algorithm with the optimal detection performance grows exponentially with the increase in the number of transmitting antennas, which makes it difficult to be used in practical application.
At present, multiple-input multiple-output (referred to as MIMO) detection algorithm has been studied widely. More typical algorithms include two types: one is linear detection algorithm focused on zero forcing (referred to as ZF), minimum mean square error (referred to as MMSE) and variants thereof; the other is non-linear algorithm focused on vertical-bell laboratories layered space-time (referred to as V-BLAST), class ML and variants thereof. Although the linear algorithm has lower complexity, it has error propagation characteristics in making a detection, which makes its performance very poor in the case of low signal-noise ratio. The V-BLAST algorithm achieves certain performance improvement over the linear algorithm, however, its complexity increases accordingly. Compared with the linear algorithm and the V-BLAST algorithm, the ML algorithm has higher complexity, but it can improve system performance significantly. More important, the ML algorithm can maintain excellent performance even in the case of relatively lower signal-noise ratio, which undoubtedly has great attraction to wireless communication systems.
In order to resolve the high complexity problem of the ML algorithm, many simplified algorithms which can decrease the complexity of the algorithm on the premise of less performance sacrifice have been proposed. More typical algorithms include sphere decoding, K-Best algorithm and variants thereof. The main disadvantages of these algorithms include that: 1) Serial operation has too many cyclic search instructions, which can improve power consumption and processing delay of programmable devices significantly and goes against real-time processing of signals; 2) The calculation complexity of the traditional algorithm is too high and its execution process relies on dynamic skip, which will decrease resource utilization rate of programmable devices greatly; 3) The incorrect constellation points searched by the previous level of antenna will effect the search of constellation points in the next level, thereby generating error propagation.
The selective spanning with fast enumeration (referred to as SSFE) which is a space-time decoding method will be explained emphatically. In the SSFE scheme, candidate constellation points at each level are chosen by selective fast enumeration method.
Specifically, in the MIMO system, assuming Nt transmitting antennas and Nr receiving antennas, a M-QAM modulation mode is used. A receiving signal y can be represented as y=Hs+n, wherein H is a channel matrix with a matrix size of Nr×Nt, s is a transmitting signal with a matrix size of Nt×1, n is white gaussian noise with a matrix size of Nr×1.
H=Q×R can be obtained by QR decomposition of channel matrix H.
Multiplying the receiving vector y by a Hermitian transpose of a matrix Q after the QR decomposition of the channel matrix H, i.e., ŷ=QHy, wherein QH represents Hermitian conjugate of the matrix Q.
An increment ∥e∥ of Euclid distance of a symbol sj estimated by ith transmitting antenna is defined as
                                      e          ⁡                      (                          s              i                        )                                      2        =                                              y            ^                    i                -                              ∑                          j              =              i                                      N              t                                ⁢                                    R              ij                        ⁢                          s              j                                                  ,wherein sj represents the detected transmitting signal of the jth transmitting antennas, Rij represents the element in the ith row and the jth column of a matrix R, and ŷi represents the ith element of the vector ŷ.
It can be seen from above that the SSFE technology provides a better space-time decoding idea and method. However, in actual situations, it is not good as the model. There are following problems in the SSFE technology in making fast enumeration: 1) When the selective fast enumeration of constellation points are performed, the results obtained by this approach exceed the scope of a constellation drawing when the constellation points of signals to be detected are located on the edge of the constellation drawing; 2) Because the determination of constellation points at the next level depends on the constellation points obtained at the previous level, all results obtained after this branch are erroneous as long as one result exceeds the scope of the constellation drawing.